The present invention relates generally to a document validator having an inductive sensor.
Documents, such as banknotes, often include magnetic or other metallic "signatures" to help detect and prevent counterfeiting. For example, inks or dyes having magnetic properties can be printed on the banknotes. Thus, portraits appearing in the center of various U.S. bills are printed entirely with magnetic ink. Similarly, an engraving which forms the printed border of U.S. bills is printed with magnetic ink. The magnetic properties are controlled to produce a defined magnetic signature or pattern associated with genuine banknotes.
Such magnetic properties can be sensed, for example, by a banknote or bill validator. Some bill validators sense the magnetic signature associated with a banknote or other document inserted into the validator by pressing the inserted document against a magnetic head or sensor. When the magnetic sensor comes into contact with the document, the sensor detects a magnetic field produced by the ink. The detected field can be used to determine the validity of the inserted document.
However, as a result of continual contact with banknotes or other documents, the magnetic head picks up dirt and other debris. The debris can contaminate the magnetic head and degrade performance of the validator if the magnetic head is not cleaned periodically. Also, the ability of the validator to handle worn or damaged notes can be reduced when contact with the documents is required to validate the notes. Moreover, bills can become jammed in the passageway of the validator if too much pressure is applied when the banknote is pressed against the sensor.
Although the use of non-contact magnetic sensors is desirable, the fact that the intensity of the magnetic field decreases as the distance of the sensor from the banknote increases previously has limited the use of non-contact magnetic sensors in banknote or bill validators.